1. Field of Invention
Rotary cutting tools.
2. Description of the Prior Art
Generally, in the manufacture of cutting tools, such as drills, reamers, thread milling cutters, hobbing tools, and the like, the tool stem and cutting head are made integral with each other, the stem being of the same high speed steel or alloy s the head. This one-piece structure is finish ground to the shape and configuration desired. Any manufacturing defect in either the stem or head renders the tool useless for its intended purpose. Sometimes it can be reprocessed to eliminate the defect, but only at a substantial cost.
One attempt to overcome this disadvantage is to form the stem and cutting head separately and of different metal, and then to join them together. Generally, in this practice, the stem is made of a cheaper steel, such as ordinary carbon steel, and the head of high speed cutting steel or alloy. To this end the cutting head is formed with an axial cylindrical shank which is received in a complementary socket in the separately made stems, though in some instances the socket is formed in the cutting head and the shank is provided on the stem.
However, in quantity production of such tools, difficulties arise in forming the stem and the head separately with such high precision consistently that they will have true concentricity and coaxial relation when assembled. To overcome this difficulty, the head and stem are often assembled prior to any grinding of the tool head or the tool stem. The configuration of some of these shanks and sockets are such that the metal of the head or stem is placed under undue stress during and after assembly. As a result, upon heating and cooling of the tool in use, and subjection of the tool to torsional stresses, fractures and deviations from concentricity often occur in the multi-piece structure. Further, if the cutting head or stem is damaged the damaged part cannot be removed and a like new part substituted therefor.
In accordance with the present invention, the tool is formed in two separate parts; for example, the stem and head of the tool are formed separately, and of different metal, with interfitting polygonal connecting parts, and then are assembled and precision finish ground to final proportions and configuration with assurance of concentricity of true coaxial relation of the head and stem. If either the stem or head is damaged or worn out, the two can be disassembled without damaged to, or marring of, the undamaged or unworn one of the two and the worn or damaged one replaced with a new one at the work site, at a considerable saving in time and cost, thereby resulting in an increase in productivity of the machine in which the cutting tool is used.
The separate parts can be heat treated independently of each other, so that both can be given the heat treatment most nearly optimum for imparting the necessary characteristics for their particular functions in the combination. The separate treatment can be carried on in different furnaces concurrently, dependent upon the type of metal, with assurance of a ore uniform product. Since each part of the tool is smaller than the whole and is of different metal, the heat treating cycle for each part can be simplified. Further, the machining cost of keeping each part straight and the cost of the necessary fixture for holding each part while machining are reduced.
Again, the life of the grinding wheels and the like used for grinding during original production is greatly increased. Scrap and reworking are less costly. If only one part of the tool is worn out or damaged, the other part can be salvaged readily, whereas salvaging of an entire one-piece tool normally necessitates the step of hard chrome plating and regrinding of the entire tool, and such plate and regrinding are expensive, both as to time and labor, and also as to the chrome metal required. With the present tool, only one part needs to be plated if a like salvage operation is to be used.
In accordance with the present invention, specific means are provided for adjusting the concentricity of the separate stem and head of the tool, so as to overcome deviations, if any, from precision in original manufacturing steps prior to grinding, and in replacement of one or the other parts of the tool,